1. Field of the Invention
The present invention relates to an inner lead bonder for bonding dies to leads which are preliminarily provided in carrier tape at stated intervals.
2. Prior Art
In the existing art, there have been known two methods for inner lead bonding. The first method works as described below. A wafer formed of the plural number of dies resulted from the cutting of the wafer into the plural number of pieces at regular intervals is placed at a set position through positioning it on a table that is driven XYZ directions. A carrier tape to be fed intermittently to the area above the foregoing table is provided. Then, the bonding is carried out by directly pressing the carrier tape onto the die by a bonding tool provided above the carrier tape.
However, this method is defective in the following point. That is, because the positional matching between the die and the lead is performed through detecting the patterns of the die and the leads by using a camera provided at the position above the carrier tape, it is difficult to detect the positional deviation of the die pattern.
Also, there are some other problems. That is, the wafer is prepared by bonding it to a plate made of ceramic, glass, or other material, by using a low melting point adhesive, and slicing it at regular intervals. Therefore, during the bonding by directly pressing the carrier tape onto the wafer as mentioned above, the heat from the bonding tool is conducted to the dies around the die that is bonded. The heat thus conducted causes the adhesive to melt. This in turn affects the die to be readily deviated from the set position. In addition, it may happen that, due to the heat, the adhesive is melted out from the slicing lines of the neighboring dies and stains those adjacent dies by spreading up to their surfaces through capillarity, etc.
Furthermore, the inner leads of the carrier tape which are to be bonded must be prevented from coming to contact with pads of the dies neighboring to the die to be bonded. For this purpose, the portion of the carrier tape where the inner leads other than those to be bonded are coming to be situated nearby the bonding tool must be provided with a curve so that the above-mentioned inner leads other than those to be bonded are kept away from the die to be bonded. Such arrangement, however, brings about the undesirable effect on the carrier tape.
The second method works as mentioned below. A table whereon a wafer is placed and that is driven in XY directions is disposed at the location spearated from the bonding position for carrier tape. Between the foregoing bonding position and the table, a spot for positioning a die is provided. This die positioning point is provided with die positioning fingers serving to position the die. Then, a piece of the die is sucked up by vacuum from the wafer by the first carrier arm, and carried to the die positioning point. There, the die is set in position by the positioning fingers. Next, by vacuum, the second carrier arm sucks up the die that is positioned as mentioned above, and carries it to the bonding position. Thereafter, the bonding operation is carried out through pressing the carrier tape onto the die from above the carrier tape by using a bonding tool.
In this method, the die is positioned at the point separated from the bonding position. Therefore, there is an advantage in it that a camera provided at the location above the bonding position is required only to detect the leads of the carrier tape alone. However, there still accompanies the problem that the positional deviation of the die occurs during the suction and during the release from suction, since the die once positioned is again carried by the carrier arm through getting sucked up.